Natural History of Upper Teesdale
6 - Origins and history of Teesdale flora
Botanists know the remarkable collection of plants of outstanding scientific interest in Upper Teesdale as the Teesdale Assemblage. Today, it is generally agreed that the majority of the ‘Teesdale assemblage of plants’ are relics, which were widespread in much of Britain in the Late-glacial period and subsequent warmer periods. Fragmentation of their, then, more or less continuous distribution patterns took place during the subsequent warmer (forest) and later wetter (blanket-bog) periods.
The high incidence of distinct local races in several species can be explained as small-scale evolutionary changes which have taken place during the long isolation of the populations in their Teesdale habitats. A further special feature of interest exhibited by several of the rarities is that taxonomically they are represented in Teesdale by local races. In some cases, the divergence from other populations of the same species is sufficiently great to warrant their reclassification as a new sub-species.Download Chapter in PDF